Transmission system for controls and signals for toll or long distance telephone circuits



Aprll 24, 1951 r GOHOREL 2,549,803

TRANSMISSION SYSTEM FOR CONTROLS AND SIGNALS FOR TOLL 0R LONG DISTANCE TELEPHONE CIRCUITS Filed Aug. 5, 1947 2 Sheets-Sheet 1 INVENTOR FER/VAND P. GOHOREL ATTORNEY April 24, 1951 F. P. GOHOREL TRANSMISSION SYSTEM FOR CONTROLS AND SIGNALS FOR TOLL OR LONG DISTANCE TELEPHONE CIRCUITS 2 Sheets-Sheet-Z Filed Aug. 5, 1947 lNVENTOR F'R/VAND P. GOHOREL cuits comprising repeater stations or not.

Patented Apr. 24, 1951 TRANSMISSION SYSTEM FOR CONTROLS AND SIGNALS FOR TOLL OR LONG DIS- TANCE TELEPHONE CIRCUITS Fernand P. Gohorel, Antony, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 5, 1947', Serial No. 766,422 In France December 20, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires December 20, 1965 12 Claims.

1 This invention relates to a transmission system for controls and signals for toll telephone circuits.

The use of voice frequency currents for the purpose of transmitting control and signal im-- pulses between exchanges or central ofiices in automatic Switching toll telephone systems has already been proposed. This method offers advantages, particularly in cases where the central offices are connected by Pupin coil loaded cir- This ensures minimum damping in the course of transmission and maximum amplification while passing through the repeater stations. However, this utilization requires special arrangements to make it impossible for the conversation currents to cause false controls or signals. Various solutions have been ofiered to prevent this unwanted action of the conversation currents but they are fraught with a multiplicity of drawbacks in actual circuit operation, even when the use of multiple frequency currents is provided.

The object of this invention is a system which, by's'imple and efficacious means, allows of trans- -mission or retransmission of controls or signals while at the same time ruling out an possibility of an unwanted action of the conversation currents.

One of the characteristics of the invention will be found in the fact that the controls or signals are transmitted by signals at a frequency 1, comprised within the voice frequency band, use being made of a common device for the reception and transmission of the signals, means being provided for the currents having frequencies different from 7" to be made unable to act on said devices.

Another characteristic of the invention will be found in the fact that the detector oscillator device connected to the parallel circuit comprises elements which are used for both detector and oscillator functions, said device normally being in the-detector condition and its changeover to the oscillator condition being made dependent on the equipment of the central ofiice with which it is associated.

Another characteristic of the invention is to be found in the fact that, when the detector-oscillator device is placed in the oscillator condition, the band pass filter of the parallel circuit to which it is connected is eliminated in order to remove the attenuation which it would cause in the transmission of the signal.

In cases where a connection is completed between one central office and another one over one or several intermediate central ofiices, it may be of value, in order to increase the speed of operation, not to have each intermediate central office retransmit the control or signal impulses.

Another characteristic yet of the invention will be found in the fact that, when a call is routed through a central oflice, the band rejection filters placed before and after said central ofiice are eliminated and a single one of the parallel circuits is kept operative in order to receive the releasing or supervisory signal.

The principles on which this invention rests will be made clear by the following description, given below as a non-restrictive example and read in connection with the accompanying drawings in which:

Figure 1 is a diagrammatic showing of two connected long distance central oflices Figure 2 is a similar diagram showing tWo terminal central offices and an intermediate central ofiice; and

Figure 3 is a circuit diagram of an embodiment of the detector-oscillator as used at an intermediate ofiice.

Figure 1 shows two toll or long distance central ofiices C11 and C12, connected by a circuit L. At central ofiice CIl, circuit L is connected, on the one hand, to a band rejecting filter EB1 and, on the other hand, to band pass filter PBl of the parallel circuit, connected to detector oscillator D01. In central office C12, circuit L is connected, in a similar fashion, to EBz and PBz'.

A frequency 1, located within the voice-frequency band, say 2,000 C. P. S., is chosen for the control and signaling impulses. In this case, band rejecting filters EB1 and E132 are so designed as not to pass the 2,000 C. P. S. frequency. Conversely, band pass filters PB1 and PB2 pass only said frequency.

Normally, when no control or signal is sent out from acentral office, the detector-oscillator device associated with it is in its detector condition.

It will now be assumed that a signal or control has to be sent from central oflice 011 to central office C12. Once the various operations that are characteristic of the signal to be sent out have been carried out in equipment E1 of C11, said equipment acts on D01 and thus causes it to change over to its oscillator condition. Under the control of E1, the oscillator is connected to the parallel circuit and an alternating current impulse at a 2,000 C. P. S. frequency is sent out over circuit L. Said impulse is received, through PB2 in D02 of CIz and retransmitted to equipment E2 in the form of a direct current impulse.

At the end of the transmission of the signal, equipment E1 causes D01 to revert to its detector condition.

The signals sent out from C12 to 011 are transmitted and received in similar fashion.

When the conversation currents are received, either in E1 or E2, they are sent over line L through filters EB1 or E132. Under such conditions, the 2,000 C. P. S. signaling frequency will be blocked and not transmitted over line L. The conversation currents other than that at 2,00% 0. P. S. can not be received in D01 or D02 due to the presence of filters P31 and PB2. As a consequence of this, all possibility, on the part of the conversation currents, to exert an action on detectors D01 and D02 is rigidly ruled out.

The directing or positioning impulses, then may be transmitted from one central ofiice to the other in the form of 2,000 C. P. S. signals, according to the process which has been described above.

Figure 2 shows two terminal central ofiices C11 and C13, as well as an intermediate central office 012. This intermediate central office comprises, on either side of equipment E2, the band rejecting filters EB'2 and E132 and the parallel circuits connected to detector-oscillators DO2 and D02 through band pass filters PB'2 and PB2.

For the case in which a connection has to be completed between central offices C11 and C13, the signals sent out by D01 or DO's will be received at DO2 or D02 and thus must be retransmitted by these last two mentioned detectoroscillators, unless special arrangements are provided at central ofiice C12.

In order to accelerate the routing of the calls, a provision may be made for the call to pass through C12 without being retransmitted.

Once the elements of E2 have been positioned by the signal (3) received by DO2, on line L2, a provision is made, within E2, for operations following said directing, the effect of which is to short out filters EB2 and EB2 and to open the one or the other of the parallel circuits of D02 or D02. One of the detectors, say DO2, remains in operation.

The signals sent out by C11 toward C13 pass through 012 without being retransmitted. At the end of the call, when a long releasing signal is sent over the line, it is received in DO2 and retransmitted in E2, in which it starts the releasing process. Filters EB'2 and EB2 are re-inserted in the lines in series and device D02 is replaced in the operative condition.

A description will now be given, with reference to Figure 3, of an embodiment of the detectoroscillator. It will be noted that one of the design pecularities is to be found in the use of the same equipment to two difierent ends, namely the reception and the generation of oscillations at a given frequency f.

The change-over from receiver to oscillator operation is efiected instantaneously and in a simple manner by the device of keeping the tubes in the same operating conditions.

This process makes it possible to obtain a good stability of operation in spite of the use of limited equipment. The amplification adjustment for one case remains unchanged for the next.

Wires 5, 8, 9, 5', 8, It, I2 and H are connected to equipment E of the toll central oflice as well as line conductors or wires 3' and 4.

In order to start the equipment, a negative potential is placed on wire 5' in equipment E. The circuit of the right hand winding of relay 3 is completed and said relay attracts its armature. By way of its work contact 32, it completes the cathode circuit of tubes 46 and 34 as follows: positive battery terminal, left hand winding of relay 3, work contact 32, filament of tubes 46 and 34 and negative battery terminal. The spring of contact 3!, associated with relay 3, can complete either the circuit of wire 8, or that of wire it. After the equipment is placed in operation, the potential placed, in E, on wire 5', is removed and relay 3 then holds its armature only through its left hand winding. If there is a break in the filament of one of tubes 46 or 34, namely if the equipment is not in a condition to operate, relay 3 drops its armature and, by means of its spring 3! and the associated rest contact, it places a potential on wire 8', which makes it possible to cause, in equipment E, the start of a trouble ring.

Normally, namely when the equipment operates as a detector, relays l and 2 are at rest, since there is no potential whatsoever on wires l2 and H. Springs H to [5, associated with relay I, close their rest contacts, as well as spring 2|, attached to relay 2.

Circuit L is connected, on the one hand, to band rejecting filter EB, made up of the series connected elements 7, ll, 6, I8 and the parallel units 8 and 9. This filter has been so designed as to pass the voice frequency currents to the exception of frequency chosen for the transmission oi controls and signals. Circuit L is connected, on the other hand, to the parallel circuit in which band pass filter PB is provided, a filter which consists of a transformer T1 and units it, 26, 22, 23. The line conductors 3 and 6 are connected to equipment E.

When a signal at frequency is received over circuit L, it can not pass filter EB but does pass filter PB and is received on potentiometer 25, the midpoint of which drives saturated tube 34. A parallel resonance or anti resonance circuit, made up of elements 3631 is provided in the plate circuit of said tube, tuned to frequency f.

The amplified voltage at the terminals of 36-31 acts through blocking capacitor 40 and.poten tiometer 42, on the grid of tube 46, which is connected as an amplifier. At the output of said tube, the amplified current is received on the primary of transformer T2. An alternating current thus is received in rectifie 49 and transformed into a direct current which circulates through the winding of relay 4, which then attracts its armature. Relay 4 having moved said armature, spring 4| which is associated thereto opens the circuit made up of wires 5 and 8 and completes the wire 5--wire 9 circuit, which makes it possible to cause, in equipment E, the carrying out of the operations which are to follow reception of the signal. At the end of the reception of said signal, relay 4 drops its armature and spring 4| resumes the position shown on the figure.

It will be noted that, due to the fact that tube 34 is saturated, the current which passes through relay 4 remains essentially constant while the voltage of the signal received may vary between widely separated limits.

When a signal must be sent out by the central ofiice with which the equipment of Figure 3 is associated, a negative battery is placed, by equipment E, on wire l2, which causes the armature of relay l to be held. The lower right hand winding of transformer T1 is connected by spring l2 of relay l and its work contact, to output transformer T2 of amplifier tube 46. The grid of tube 34 is connected, by way of spring ll of relay l,

to the tuned circuit 36-31. Said tube 34 thus will operate as an oscillator at the frequency of circuit 36-31. The voltage present at the terminals of 363l is applied through capacitor 40 and potentiometer 42 to the grid of tube 46.

The current at frequency f, amplified by tube 46, finally is received over wire 51. Due to the fact that relay 2 is at rest, its rest contact 2! shorts out the lower right hand winding of transformer T1. Signaling currents at frequency f can not be sent over the line.

When the signal must be sent over the line, a potential is placed, in equipment E, on wire II, which causes relay 2 to be energized. Rest contact 2| is open and a current at frequency 1 passes through the lower right hand winding of T1 (the value of resistor 56 is considerable). This current is induced in the left hand winding of T1 and directly transmitted over circuit L, with contact I of relay I closed and contact 13 open. When transmission of the signal is to cease, the potential is removed from wire H. Relay 2 drops its armature and, by way of its contact 2|, puts an end to the sending of the signal through the winding of T1.

It will be noted that, during the transmission of a signal, band pass filter PB is eliminated, which makes it possible to reduce the attenuation which it would cause in the transmission of said signal.

Once the transmission of the signal is over, the potential is removed from wire l2. Relay l drops its armature and the equipment is restored to its detector condition.

What is claimed is:

1. In a telephone system having a plurality of oflices and interconnecting line circuits, means for transmitting control signals between offices at voice frequency comprising at a station a detector-oscillator device, means normally connecting said device to the line circuit of that olfice through selective means to receive only the frequency of said control signal, means connecting said office and line circuit for the voice band exclusive of said control signal frequency, and means controlled from said office to cause said device to change over and transmit oscillations at said control signal frequency over said first mentioned connecting means to said line circuit.

2. Signal transmitting means according to claim 1, including a control relay enabling the predetermined operations at said office, and means including a rectifier for coupling the output of said detector-oscillator device to said control relay.

3. Signal transmitting means according to claim 1, in which the selective means in the first mentioned connecting means includes a filter passing the signal control frequency, coupled by a transformer to said detector-oscillator device, said transformer having a pair of windings for transmitting and receiving said frequency and another pair of windings connected to the input and output respectively of said device.

4. Signal transmitting means according to claim 3, wherein the connection between the one secondary and the input of said device is normally closed, and the connection of the other of said pair and the output of said device is normally open.

5. Signal transmitting means according to claim 4, including relay means controlled from said ofiice to effect changeover from reception to transmission of said control signal frequency.

6. Signal transmitting means according to claim 1, including means under control from said office whereby the selective means in said first mentioned connecting means is eliminated during signal transmission from said detector-oscillater.

7. Signal transmitting means according to claim 6, wherein the eliminating means comprises a short circuit of the selective means.

8. Signal transmitting means according to claim 1, wherein said system includes one or more intermediate repeating ofiices andthe latter are each equipped with both said selective means on either side toward a cooperating ofiice.

9. Signal transmitting means according to claim 8, wherein control means at an intermediate oflice enables direct relaying therethrough of control signal frequencies by elimination of the voice band selective means.

10. Signal transmitting means according to claim 9, including control means for eliminating from the intermediate oflice the parallel selective means and retaining a single one thereof for the subsequent control of the calling connection.

11. Signal transmitting means according to claim 1, wherein said detector-oscillator device comprises a convertible detector tube having a normally inoperative frequency determining oscillatory circuit, with means for rendering it operative and includes means for maintaining said tube in operating condition. 1

12. Signal transmitting means according to claim 11, including an amplifier tube coupled to the output of the detector-oscillator tube and means for maintaining both tubes in operating condition.

FERNAND P. GOHOREL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date 

